Table of contents

The holographic interferometry bench presented in the paper is different from conventional set-ups in that it uses a second reference source. This source can be adjusted in position, and the phase of its radiation is continuously adjustable.

This improvement increases the possibilities of applications of interferometry as it authorizes experiments impossible with the conventional interferometer or a current holography set-up. The operating mode calls upon the two techniques of reference hologram and of double exposure.

Three examples of application on actual cases are presented, and illustrated by photographs.

Facilities of computer generated Fourier holograms are envisioned with the synthesis of a computer holographic memory in view.

The computing process described is applicable to a class of objects made up of binary points. A relatively small number of samples is used, and this without any phase encoding. A double threshold amplitude saturation is performed on the Fourier transform, thus optimising the efficiency and S/N ratio, both studied on a theoretical model and by numerical simulation. Non linearities are finally cut out by a very simple filtering process implemented in incoherent light, the result being synthesis of a continuously varying grey level function. A 3 x 3 mm Fourier hologram of a 64 x 64 binary point object restores a highly acceptable image.

Nevertheless the photoreduction is slow and limits storage density. A direct point by point discretely recorded hologram is proposed. For this purpose, we describe two alternate systems of a real-time computer-controlled optical microprinter. Using the above methods, characteristics are outlined for computers holographic memories.

The free spectral range of two Fabry-Pérot etalons in series as a function of their spacing ratio is systematically investigated by a new method, called method of « forbidden zones ». Its properties and directions for use are discussed. It gives the best ratios and surely. The important simplification of calculations and the reliability of results become primordial advantages in the case of more complicated chains. Other applications may be hoped.

A study has been made of the transmission characteristics of a Fabry-Perot interferometer as modified by the asymmetric surface defects present on the plates. Asymmetric line profiles can be obtained if the error in the plates is not symmetrically distributed about the mean planes of the plates. Peak irradiance and shift of fringe from its integral order position have been tabulated. Such investigations are of interest in a number of problems in high resolution spectroscopy.

Recent experimental measurements made by Hutley in the visible region on holographic diffraction gratings have revealed that serious discrepancies exist between predictions based on an infinite conductivity grating theory and the actual behaviour of optical gratings. It is shown here that these discrepancies can be removed if finite conductivity effects are taken into account by the grating theory.

Grids of efficiency curves calculated for gratings having sinusoidal profiles covered with aluminium are given here. It is shown how these curves may be used to estimate the groove depths of holographic gratings from their experimental efficiency curves, using as an example the data Hutley.

The importance of profile distortion on the form of the efficiency curves is made evident. Theoretical data is given on the best mount for holographic gratings, and also on the range of groove depths which gives them the best blaze.

This paper describes a Fabry-Perot interferometer design using a very small order of interference.

The scanning is obtained by an elastic deformation of a metallic ring.

All sources ofinstability have been carefully studied.

This interferometer is intended for use at an astronomical telescope. The dimentions of the ring have been computed theoretically in order to minimize flexure due to the weight of the different parts of the morinting in all orientations.

The 40 cm coude equatorial telescope of the Nice Observatory is presented as a new solar instrument.

This telescope, an old instrument renewed on a financial support from I. N. A. G., is briefly described. Mechanical and optical improvements are then detailed, in particular the performance, in the optical laboratory of the Nice Observatory, of two mirrors in cervit, and a cooled focus device for solar observations.

The site, which is sunny around 2 800 h every year, is comparable for this point of the best european sites tested in J. O. S. O. operation. The first solar granulation plates obtained in september 1973 show some details reaching the theoretical resolution limit.

This telescope is now used by the workers of the Nice University Astrophysical Laboratory, directed by F. RODDIER.